1. Field of the Invention
This invention relates to the field of magnetic recording and more particularly to an improved floppy disk of the type used in digital data storage units and a method of manufacturing the same.
2. Description of the Prior Art
Widely used in the computer industry is a removable and interchangeable data storage medium assembled by enclosing a circular disk of flexible material coated with magnetic particles within an envelope. These assemblies are known in the trade as "floppy disks." A method of constructing floppy disk assemblies is described in U.S. Pat. No. 3,668,658 issued to Flores, et al. Both the envelope and the flexible recording disk contained therein, as described in that patent, are formed with a circular aperture passing through their respective centers. In accordance with that patent, the diameter of the circular aperture formed through the envelope is larger than that formed through the flexible recording disk. A larger aperture is formed in the envelope to permit engagement of the recording disk contained therein by a drive spindle of an apparatus used to write data to and read data from the flexible disk. Engagement of the flexible recording disk by the drive spindle is necessary to permit its rotation within the envelope by the reading and writing apparatus so that all the storage area of the circular data tracks thereof may be accessed. This rotation of the flexible recording disk requires the disk material immediately surrounding the central aperture to transmit the total force needed to rotate the disk within its envelope. Furthermore, because the envelope which contains the flexible recording disk is larger than the outer diameter of that disk, the disk in an assembly removed from the reading and writing apparatus is free to move within its envelope. Thus, upon reinsertion into the reading and writing apparatus, the central aperture in the flexible recording disk may not be in alignment with the spindle thereof. Consequently, the spindle of the reading and writing apparatus is designed to enter a misaligned central aperture in a flexible recording disk to apply a force to the material immediately surrounding it and cause the aperture to become centered thereabout when engagement is completed.
Thus, due to the stress applied by the forces of engagement and rotation, it has been observed that the material of the flexible recording disk immediately surrounding the central aperture becomes damaged in the normal course of an assembly's use. Ultimately, this damage may become so extensive as to render the floppy disk assembly totally inoperable. However, even if such damage is not so severe as to render the floppy disk assembly totally inoperable, it may be the source of reading failures upon dismounting and remounting the floppy disk assembly in the reading and writing apparatus. This type of reading failure may be caused by misalignment of a flexible recording disk having a damaged central aperture with the spindle which engages it. Such misalignment, which causes the center of previously written data tracks to be displaced from the center of rotation of the spindle, may cause the data stored thereon to be unreadable due to excessive oscillation of the data track with respect to the reading apparatus. This type of failure may sometimes be apparently cured by merely again dismounting and remounting the floppy disk assembly.
A means for reducing this damage includes mechanically reinforcing the region of the flexible recording disk immediately surrounding the central aperture. One such reinforcement structure is described in U.S. Pat. No. 4,052,750 issued to Barber, et al. The structure and method described there, consists of adhesively bonding a punched annular-shaped piece of structural material to the surface of the flexible recording disk about its central aperture. That patent further describes that the reinforcement, so applied, must have certain frictional properties to permit proper mechanical engagement by the reading and writing apparatus and certain electrical properties to allow dissipation of static electrical charges which may build up on the flexible recording disk. However, fabricating floppy disk assemblies in accordance with that description makes it difficult to obtain consistently good registration between the edges of the central aperture in the flexible recording disk and the edges of the annular-shaped structural reinforcing member. Furthermore, long term usage of floppy disk assemblies constructed in accordance with that description result in the adhesive bonding the annular-shaped reinforcing member to the surface of the flexible recording disk oozing from between those members to project within the diameter of the central aperture. Consequently, in time, the spindle of the reading and writing apparatus engaging the flexible recording disk becomes contaminated with that adhesive.